In today's market place there is virtually an endless variety and makes of the usual home television sets. As a result of this, and the fact there is no standardization of the sizes and shapes of the control knobs used on television sets, there are an almost infinate variety of control knobs used throughout the industry.
The lack of standardization is no more evident than in the case of television tuners or channel selectors, for not only do control shaft lengths vary, but the position of the flat land which the control knob engages for rotation varys on the shaft so that its angular position, when a given channel is selected may and does vary making it impossible to determine, from the channel indicator on the knob, what channel has been tuned unless the channel indicator and knob have been precisely designed for use with a given tuner.
FIG. 1 schematically illustrates the mentioned problem. As shown, the tuner 1 is operated by a shaft 3 having a flat land 5, or other discontinuity which is adapted to engage a similar land or discontinuity located in the bore of a sleeve of an operator knob (not shown) which turns the shaft 3. Also connected to the shaft 3 is some form of detent means, illustrated as a detent wheel 7 and a spring biased detent ball 9 so that as the tuner is rotated from one angular position to another it is releasably locked in the selected angular position. The control knob which is originally furnished with the tuner, whatever make or brand, is always so designed that when it is installed on shaft 3 the channel indicators will align with the detents and also will align with the tuner so as to indicate to which channel the tuner is set. Thus, the tuner and knob are specifically matched to each other.
Unfortunately, it is a fact of life that T.V. tuner knobs do get broken and lost. A conservative estimate would be that, after several years, at least one out of five television sets end up with a broken or lost tuner control. When consideration is given to the number of sets sold and in use in the world, it becomes immediately evident that the market for replacement television tuner knobs is substantial. However, due to the lack of standardization for such knobs, the only sources for such replacements is the individual manufacturer of any given brand of television and even here it is necessary to order replacements for individual sets because every manufacturer markets a wide variety of styles and models of sets most of which do not share common tuner control knobs or even tuners.
The brunt of the lack of availability of replacement control knobs for television tuners is, as is often the case, borne by the consumer who when faced with the problem of a lost or broken tuner knob must order the knob directly from the manufacturer of the particular set or must attempt to obtain a replacement from a distributor of the particular product or resort to the usual T.V. repair service in an effort to correct the situaition.
Since it is impossible for distributors or television repair shops to stock every knob for every television set, the end result is that some make-shift substitute knob is offered to the consumer which may not fit properly or properly identify the channel selection of the tuner or, alternatively the unfortunate consumer must wait for eons of days until the proper knob can be ordered and obtained from the manufacturer of the particular brand of set in question. Even then, more often than not, the part is not available for one reason or another, so a make-shift substitute is the end result.